Process for connecting circuits and adhesive film used therefor

ABSTRACT

An adhesive film comprising (a) a liquid epoxy resin, (b) a solid resin having one or more functional groups, (c) a microcapsule type curing agent, and if necessary (d) a coupling agent, is effective for connecting semiconductor chips and wiring boards under heat and pressure.

This application is a Continuation application of application Ser. No.490.915, filed Mar. 9, 1990, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a process for connecting semiconductor chipsto circuits on a substrate and an adhesive film used therefor.

As a method for attaching semiconductor chips having electrodesprojecting from the main face (such as IC's with bumps) to a wiringsubstrate, it is known to apply an adhesive between the electrodes ofsemiconductor chips and the substrate surface where the correspondingcircuit terminals are formed, and the IC chips and wiring substrate arepressed against each other so that the electrodes of the IC chips andthe wiring substrate will become conductive and be bonded to each other.Regarding the adhesive used for the above purpose, there are a casewhere an anisotropic electroconductive adhesive prepared by mixingelectroconductive particles in an insulating adhesive is used and a casewhere an insulating adhesive is used.

Anisotropic electroconductive adhesives have a problem in the retentionof insulating performance since there may occur short-circuiting due tothe presence of electroconductive particles between the adjoiningcircuits when, for instance, connecting high-density circuits. Also,since the electroconductive particles are generally hard, this type ofadhesive involves problems of possible cracking of IC chips in thepressing step at the time of connection and a tendency to cause arupture in the wiring protective coat.

Regarding a procedure for the way of application of an insulatingadhesive, there is known, for instance, a method in which alow-viscosity curing adhesive such as an ultraviolet-curing typeadhesive is applied on the circuits and these circuits are contactedwith each other through fine unevenness on the circuit surfaces bypressing at the time of connection to thereby effect desired electricalconnection, and then the adhesive is cured to complete the connectionand bonding, with the superfluous portion of adhesive being removed outof the circuits (see, for example, Japanese Patent Publication No.46-43732, and NIKKEI MICRO-DEVICES, June, 1987, issue, page 65, NikkeiMcGraw-Hill).

Among these types of adhesives, those made of thermoplastic materialsare simple in use for connection but unsatisfactory in heat resistanceand connection reliability. Attention is therefore paid to the curingtype adhesives.

Curing of adhesive has been generally performed by applying a form ofenergy such as heat and light (ultraviolet rays, electron rays, etc.).In the case of heat curing, it can be effected by heating and pressingthe adhesive between hot plates. In the case of ultraviolet-curing, atransparent plate such as glass plate is used as one of the pressingplates and ultraviolet rays are applied through the transparent plate.

Practical use of the conventional types of adhesives has the problemssuch as pointed out below.

(1) Because of wide variety in height of projecting electrodes from themain face, a high connection reliability can not be obtained.

The number of projecting electrodes per chip may vary from 10 to as muchas 500, and the height of these electrodes is usually in the range ofabout 1 to 50 μm. It is difficult to form such a large number ofelectrodes with uniform height, for example, with a scatter of less than0.5 μm in height. When the height of projecting electrodes isnon-uniform, although the electrodes with a large height can easilycontact the circuit surface on the substrate, the electrodes with a lowheight may fail to reach the circuit surface to form a spacetherebetween, making it unable to obtain an electroconductiveconnection.

(2) With the method of the type in which a liquid adhesive is applied onthe electrodes, it is difficult to control the coated adhesive thicknessuniformly, and there may take place such a phenomenon as shortage ofadhesive at the connecting portion or generation of air cells, resultingin unsatisfactory connection reliability.

Further, in this type of method, the adhesive used needs to be liquidwith low viscosity for the operational reason. Therefore, the adhesiveused in this method is usually prepared by using a low-molecular weightmaterial and subjecting it to a curing reaction to turn it into ahigh-molecular weight substance, or by diluting a high-molecular weightmaterial with a solvent or the like.

In the case of the former method, since a low-molecular weight materialis suddenly turned into a high-molecular weight substance, there takesplace an excess degree of cure shrinkage, which generates a residualstress at the connecting portion to make its thermal impact resistanceunsatisfactory. In the case of latter method, there arises the problemof environmental pollution as the solvent is dried away. Also, theresidual solvent is gasified when heat and pressure are applied at thetime of connection, causing generation of air cells. It is thusimpossible with these methods to obtain satisfactory connectionreliability.

(3) When viewed from the adhesive curing system, the ultraviolet-curingmethod is subject to restriction on the type of substrate employedbecause the substrate used in this method must be permeable toultraviolet rays.

It is hardly possible with the heat-curing method to satisfy the twoantithetic property requirements, namely keeping quality and quickcuring property at the same time. For instance, this method is very poorin performance of such operations as curing by long-time heating underpressure or short-time coating by mixing a curing agent just before use.

In the case of the method using a thermoplastic material, there is theproblem of unsatisfactory heat resistance, and also it is impossible tosufficiently remove the adhesive from the contact area betweenelectrodes and circuits since the drop of viscosity is insufficientunder the practical temperature and pressure at the time of connectionbecause of a high molecular weight, such as several tens of thousands,of the material, so that a secure electrical connection can not beobtained.

(4) Another problem is the method of regeneration or renovation offaulty parts.

For example, in the case of liquid crystal display module (hereinafterreferred to as LCDM), several to several tens of semiconductor chips perLCDM are connected on a transparent electroconductive glass plate(substrate) either directly or through a tape carrier (generally calledTAB), and after passing a live test, the assembly is offered as aproduct module.

Since the live test covers the synthetic tests for semiconductor chips,connected portions, circuitries, etc., it is necessary to conduct thetest on the assembly in a state close to that of the finished product.

When an abnormality is detected in the live test, the abnormal part(s),e.g., defective semiconductor chip(s), is(are) replaced with normalone(s), and the connecting operation must be performed again. In thiscase, it is possible to remove the abnormal part(s) relatively easilywhen a conventional thermoplastic adhesive has been used since suchadhesive can be lowered in its adhesive force by slight heating. In thecase of curing type adhesives, however, since the connected area isfirmly bonded and since the adhesive, because of its reticulated(cross-linked) molecular structure, loses little of its adhesive forceeven when heated and the adhesive is hardly soluble in solvents, thereare great difficulties effecting the removal of defective part(s).

For removing the defective part(s), therefore, there has been noalternative but to dip the faulty connected portion in a solvent or anacid or alkaline solution for effecting swelling or decomposition of thereticulate structure or to resort to a forcible removing means, such asscraping-off with a knife.

Use of such forcible means, however, may give damage to the normalconnections and wiring around the faulty part and would also inevitablyleave a part of adhesive unremoved, making it unable to obtain areconnection with high reliability. Accordingly, renovation has beenvery difficult and the yield of products would be lowered, leading to anincreased production cost.

SUMMARY OF THE INVENTION

In view of said problems in the prior art, the present invention isdesigned to provide a process for connecting circuits with markedlyimproved connection reliability and workability and an adhesive filmused therefor.

The present invention provides a process for electrically connectingcircuits by interposing an insulating adhesive between two opposingcircuits in which at least one of the circuits formed on an insulatinglayer has a plurality of electrodes projecting from the main face, saidprojecting electrodes having deformability under pressure in the circuitconnecting operation, said adhesive comprising (a) a liquid epoxy resin,(b) a solid resin having one or more functional groups and (c) amicro-capsule type curing agent as essential components and having afilmy form with a thickness of 50 μm or less and a volatile content of0.5% or less, and further characterized in that the adhesive issubstantially cured after the projecting electrodes have been contactedwith the opposing circuits under heating and pressure at the time ofconnection.

The present invention also provides a process for connecting circuits,comprising the steps of forming a filmy adhesive layer composedessentially of a liquid epoxy resin, a solid resin having a functionalgroup and a micro-capsule type curing agent on the pressure-deformableprojecting electrode-formed side of a semiconductor wafer formed with aplurality of integrated circuit elements having electrodes projectingfrom the main face; cutting said wafer along with the adhesive layer toform chips; positioning the projecting electrodes of said chips inregister with the opposing circuits on a wiring substrate with saidadhesive layer interposed therebetween; and substantially curing theadhesive after contacting the projecting electrodes with the opposingcircuits by applying heat and pressure to said chips and wiringsubstrate.

The present invention is further intended to provide a process forelectrically connecting semiconductor chips by interposing a curing typeadhesive between the electrodes of semiconductor chips and the circuitson a substrate, characterized in that a live test is conducted on thesemiconductor chips and substrate circuits under pressure while theadhesive is still in a half-cured state, and then the adhesive is curedunder heating and pressure.

It is also envisaged in this invention to provide an adhesive filmusable for said connecting process, said adhesive film comprising asessential components (a) 20 to 80% by weight of a liquid epoxy resin,(b) 80 to 20% by weight of a solid resin having a functional group, (c)a micro-capsule type curing agent having an average particle size of 10μm or less, and (d) a coupling agent, and further characterized in thatthe film thickness is 50 μm or less, the volatile content is 0.5% orless and the hydrolytic chlorine ion concentration after curing is 20ppm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic sectional views showing the steps in a circuitconnecting process according to the present invention.

FIG. 2 is a graph showing the pattern of change of viscosity of theadhesive in the circuit connecting operation.

FIGS. 3 to 6 are schematic sectional views showing the states of contactwith a circuit preferred in the present invention.

FIG. 7 is a schematic sectional view showing a state where an adhesivelayer has been formed on a wafer.

FIG. 8 is a schematic perspective view showing a state where theadhesive-applied semiconductor chips have been positioned on a circuitsubstrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereinafter be described more particularlywith reference to the accompanying drawings.

FIG. 1 illustrates, in schematic sectional views, the situations in acircuit connecting process according to the present invention, and FIG.2 is a graphic illustration of the change of viscosity of the adhesivein the process. Letters (a), (b) and (c) in FIGS. 1 and 2 indicate thesequential steps in the connecting process.

Referring first to FIG. 1(a), there is shown a situation where a layerof an adhesive 5 was formed between the electrodes 2 projecting from themain face 6 of an electric part 1 (e.g., a semiconductor chip) and thecircuits 4 provided on an insulating substrate 3 made of glass,synthetic resin or the like, and the connecting points of saidprojecting electrodes 2 (generally called "bumps") and the correspondingcircuits 4 were positioned.

The adhesive 5 used in the above process is preferably in the form of afilm which is solid at temperatures close to room temperature and has nosupport. But it is possible to use a separable substrate as support, andin this case, such support may be removed after it has once beenattached to the side of said projecting electrodes 2 or circuits 4.

The viscosity of the adhesive in this state is as indicated by (a) inFIG. 2. This adhesive is easy to handle as it takes a solid film-likestate.

As the point of (b) is reached, the projecting electrodes 2 and thecorresponding circuits 4 are brought into contact with each other underheating and pressure, and the adhesive 5 lowered in viscosity by rise oftemperature is removed outside of the contact area. The scatter inheight of projecting electrodes from the main face is eliminated byheating and pressing in the connecting operation owing topressure-deformability of said projecting electrodes 2. In thisoperation, it is necessary that all of the electrodes to be connected onthe main face 6 of electronic part 1 are at least contacted with thecorresponding circuits 4. Regarding the heating and pressing conditionsfor attaining this, heating should be conducted at a temperature of 40°to 250° C. (preferably 70° to 200° C., more preferably 100° to 180° C.),while the pressure applied should be 1 to 100 kgf/cm² (preferably 5 to70 kgf) based on the area of main face 6 of electronic part. It isdesirable that the amount of pressure applied per one projectingelectrode be adjusted to 1 kgf/cm² or less (preferably 0.5 kgf) for thefollowing reason.

When the process is carried out at high temperatures, there tends tooccur break or crack of electronic part 1 due to lack of heat resistanceof the material of said electronic part, and when the process isconducted at low temperatures, a long time is required for curing of theadhesive, resulting in poor workability in the connecting operation.When the pressure applied is high (above the above-defined range), thereis a possibility of causing mechanical break of electronic part 1,substrate 3 and/or circuits 4, while when the pressure is low, contactbetween electrodes 2 and corresponding circuits 4 may becomeinsufficient, inviting unsatisfactory connection reliability.

Various methods, such as mentioned below, (are available) for affordingpressure-deformability to the projecting electrodes 2; (an extendablematerial) (for example, the materials having an elongation of 40% ormore, shown in METAL DATA BOOK, p. 155, 1984, compiled by JapanMetallurgical Society and pub. by Maruzen Co., Ltd.) (such as gold,solder, copper, aluminum, silver, lead, titanium or the like is used asthe electrode material); (fine unevenness is formed at the end of theconvex electrode) as shown in FIGS. 3 and 4 to reduce the portion to bepressed (deformed portion); the grain boundary structure at the time ofplating is enlarged. (It is preferred to use the above-describedtechniques in combination.) Also, the electrodes may be formed with apressure-deformable material such as a thermoplastic material and theirsurfaces coated with a metal.

It is also possible to employ spacer electrodes for gap adjustmentobtained by making part of the projecting electrodes on the main face 6smaller in height than the other pressure-deformable electrodes and byusing a hard material for such electrodes. (Such spacer electrodes arepreferably provided at four diagonally opposing corners on the main faceof each IC) (chip for allowing uniform pressing.) These spacerelectrodes may be either electroconductive ones or insulating dummyelectrodes.

It is also effective to form unevenness on the circuit surface on thesubstrate side as shown in FIG. 5 as this increases the points ofcontact.

No specific restrictions are imposed on the arrangement of projectingelectrodes on the main face 6, but it is preferred to (provide on theaverage three or more electrodes at the periphery or on the entirety ofmain face) 6 so that uniform pressing may be effected in the connectingoperation.

A typical method for performing heating and pressing in the process ofthe present invention is to apply pressure while heating with a heatsource (not shown) provided outside of electronic part 1 or/andsubstrate 3. (In the step (b), the adhesive is reduced in viscosity byheating to facilitate deformation of the projecting electrodes, theircontact with the corresponding circuits and removal of the adhesive,thus enabling connection with high reliability.) Regarding the reductionof viscosity of the adhesive in the step of FIG. 2(b), the lower thelowest viscosity that the adhesive can have, the more desirable for theabove operations. For this, it is expedient to select the adhesive filmcomposition and the working conditions for connection so that theadhesive viscosity will become less than 1×10³ poise (P), preferablyless than 1×10² P.

In the above step (b), projecting electrodes 2 and correspondingcircuits 4 are in an electrically conductive state as they are contactedunder pressure, while the adhesive is in a half-cured state. Therefore,a live test may be conducted in this state to eliminate the faultypart(s). Also, after conducting a live test under the condition oflowest temperature at which electric conduction can be obtained betweenelectrodes 2 and circuits 4 under pressure, the temperature may beelevated to accelerate curing of the adhesive (step (c) describedlater).

According to this method, regeneration (removal and reconnection) of thefaulty part(s) using a curing type adhesive, which has been problematicin the prior art, can be accomplished very easily since such operationcan be performed while the adhesive is in a half-cured state.

The "live test" referred to in this invention means the tests forfunctions and working conditions under electrification, which include,for example, conduction test and short-circuiting test.

In the case of afore-mentioned LCDM for instance, the live test coversan intermediate test of product in which the half-completed product iselectrified to check for the faults in display, e.g., omission oroverlapping of display lines, abnormality of brightness, and balance ofcoloration.

According to the present invention, since electric conduction betweenthe electrodes of a semiconductor chip and the corresponding circuits ona substrate can be obtained by applying pressure while the adhesive isin a half-cured fluid state, it is possible to carry out the live testbefore the adhesive is cured.

Since the adhesive before used for the connecting operation is notadvanced in reticulation, removal of faulty part and reconnection can beeasily accomplished.

It is possible to perform the principal connection by conducting anadhesive curing reaction by heating or other means after passing thelive test.

According to the process of the present invention, as it is of a systemin which electrodes and circuits are bonded to each other with alow-viscosity adhesive, there is little fear of suffering from adhesionof dust or formation of oxide film, and it is possible to makedeterminations at many points at high speed under a stable condition.

The process has been described above by taking up the case ofapplication to semiconductor chips, but the process can as well beapplied to a live test for the products in the form of wafer before madeinto chips or to an intermediate test in mutual connection of wiringboards.

In the succeeding step (c), heating and pressing in the step (b) arecontinued to cause a sharp rise of viscosity of the adhesive byactivating the micro-capsule type curing agent in the adhesive as shownin FIG. 2. The shorter the time of these steps (b-c), the better for theoperational convenience. A time of less than 60 seconds, preferably lessthan 30 seconds is recommended for these steps in the practicaloperation. After the adhesive has been substantially cured with rise ofviscosity (step (c)), pressure is removed, thereby completing theconnecting operation according to the present invention.

The connecting process according to this invention has been describedabove concerning the case of connecting an electronic part havingelectrodes projecting from the main face (e.g., IC chip with bumps) to awiring substrate, but in case the electronic part surface to beconnected has no projecting electrodes and presents a flat main face oris recessed, the necessary part of each circuit on the wiring substratemay be raised up to constitute a protuberant electrode to thereby effectdesired connection (FIG. 6). It is also possible to provide projectingelectrodes on the opposing sides of both electronic part and wiringsubstrate.

In the following, there will be described another embodiment of theprocess of the present invention which is designed capable of performingconnection of chips to a substrate while preventing scattering of chipsat the time of cutting of semiconductor wafer.

Semiconductor chips have generally been produced by cutting inlattice-like strips a wafer made by forming simultaneously amultiplicity of circuit patterns on a disc made of silicon singlecrystal or such.

For cutting the wafer, a method is popularly used in which the wafer isfull-cut in the thickness direction at high speed by using a so-calleddicing saw having a rotary cutting edge made of diamond or likematerial, because the chips made by this method have a high dimensionalprecision.

In this method, usually an adhesive sheet is used for preventingscattering of chips during the full-cutting operation.

A problem involved in this method is that since the dicing saw isrotated at such a high speed as several thousand to several tens ofthousand r.p.m. when cutting the wafer, the adhesive sheet is requiredto have a high adhesive force that can stand high-speed rotation of thedicing saw, but in the succeeding step where the chips are separatedfrom the adhesive sheet, high adhesive force makes it difficult toseparate the chips, and if the chips are forcibly separated, theadhesive could stay adhering to the chip surface, jeopardizing the useof the chips for semiconductor devices which are essentially required tokeep free of contaminants.

In order to eliminate said problems of the prior art, the presentinvention provides an improved process for connecting circuits,comprising the steps of forming an insulating adhesive layer on theelectrodeformed side of a semiconductor wafer having a plurality of ICelements formed thereon; cutting said wafer together with the adhesivelayer to make the adhesive-applied chips; positioning said chips on awiring substrate with the adhesive layer interposed therebetween; andbringing the projecting electrodes into contact with the correspondingcircuits under heating and pressure and then substantially curing theadhesive.

The process of this invention will be described more particularly withreference to FIGS. 7 and 8.

FIG. 7 is a schematic sectional view illustrating a situation where anadhesive layer 5 has been formed on a wafer 7.

Said wafer has formed on its principal part a plurality of circuitpatterns which are, for example, lattice-like in shape and formed withprojecting electrodes which are deformable by pressing.

Adhesive layer 5 can be formed by spreading an adhesive in the form of afilm and attaching it to the wafer surface by using a roll or othermeans. This operation is very easy to perform because of appropriateadhesiveness of the adhesive, and it is also possible to apply anauxiliary means such as heating.

The wafer formed with an adhesive layer as shown in FIG. 7 is full-cutalong with the adhesive layer by using a dicing saw or other suitablemeans to obtain the chips with adhesive.

FIG. 8 shows schematically in perspective a situation where an adhesivelayer 5 has been formed over the electrodes 2 projecting from the mainface of a bump-having IC 8 obtained in the manner described above, andsaid projecting electrodes 2 and the corresponding circuits 4 on thesubstrate 3 have been positioned and set in place. Thereafter, viscosityof the adhesive is reduced by heating and pressing, and after saidelectrodes 2 and circuits 4 have been sufficiently and correctlycontacted with each other, the adhesive is substantially cured.

According to the present process, a single adhesive can serve both forprevention of scattering of chips at the time of cutting of wafer andfor the operation of connecting the chips to a substrate. This canunnecessitate the step for separating the adhesive tape or such used atthe time of chip cutting in the conventional methods and thus enablesmarked simplification of the working process.

The adhesive layer used in the present invention is the one taking afilmy state at normal temperature and having a thickness of 50 μm orless and a volatile content of 0.5% by weight or less. When thethickness of said adhesive layer exceeds 50 μm, it becomes necessary toremove a large volume of adhesive from the connecting electrode area byheating and pressing in the connecting operation. This makes itdifficult to obtain a good connection and leads to a reduced connectionreliability. When the volatile content exceeds 0.5% by weight, theretakes place voluminous generation of air cells by heating and pressingin the connecting operation, resulting in a reduced connecting area ofelectrode and unsatisfactory connection reliability.

For the above reason, the volatile content is preferably adjusted to0.1% or less. In the present invention, measurement of volatile contentwas made by pyrolysis gas chromatography at 100° C.

The thus obtained adhesive film is cured and then immersed in purewater. The treatment is preferably carried out so that the concentrationof chlorine ions determined from ion chromatographic analysis of theextract after 10-hour treatment at 100° C. (hydrolytic chlorine ionconcentration) will be 20 ppm or less (preferably 10 ppm or less, morepreferably 5 ppm or less), because the above-defined range of chlorineion concentration enables prevention of corrosion of the connectedcircuits to enhance connection reliability and can also improve thereaction rate at the time of curing of the adhesive film to realize areduction of connecting temperature and time. An improvement ofconnecting workability is also provided.

As for the other properties of the adhesive after curing used in thepresent invention, it is desirable that the concentration of eachimpurity ion (Na⁺, K⁺, SO₄ --, etc.) is less than 20 ppm, the modulus ofelasticity is below 10,000 kgf/cm² and the coefficient of thermalexpansion is less than 2×10⁻⁴ /°C.

When the concentration of any impurity ion other than hydrolyticchlorine ion is higher than 20 ppm, corrosive deterioration of theconnected portions will be promoted. Also, when the modulus ofelasticity exceeds 10,000 kgf/cm² or when the coefficient of thermalexpansion is higher than 2×10⁻⁴ /°C., the thermal stress generated atthe connected portion increases to render the connected portion liableto separate under stress.

The materials for obtaining the adhesive tape used in the presentinvention will be described below.

(a) Liquid epoxy resin

Liquid epoxy resins usable in the present invention are the compoundshaving two or more epoxy groups in one molecule. It is possible to useall known types of liquid epoxy resins. Typical examples of such liquidepoxy resins are polyglycidyl ethers of polyhydric phenols such asbisphenol epoxy resins derived from epichlorohydrin and bisphenol A orbisphenol F, and epoxy novolak resins derived from epichlorohydrin andphenol novolak or cresol novolak. Other examples of said liquid epoxyresins include polyglycidyl esters of polycarboxylic acids, alicyclicepoxy compounds, polyglycidyl ethers of polyhydric alcohols, andpolyglycidyl compounds of polyvalent amines. These compounds may bepartly modified in their structure with uretane or such. Also, they maybe used either singly or in combination.

The term "liquid" referred to in the present invention denotes the stateat normal temperature (40° C.). For example, in the case of bisphenolepoxy resin which is a preferred material for use in the presentinvention, such epoxy resin has a molecular weight of 500 or less and anepoxy equivalent of 270 or less. It is desirable that the epoxy resinused in this invention is high in purity, that is, reduced inconcentration of impurity ions (Na⁺, K⁺, SO⁻⁻, etc.) or hydrolyticchlorine ions to the level below 300 ppm for each impurity, because lowcontent of impurity ions is helpful for preventing corrosion ofconnected circuits and accelerating the curing reaction.

(b) Solid resin having a functional group

Another resin used in the present invention is required to be solid atroom temperature (25° C.) and have a functional group such as carboxylgroup, hydroxyl group, vinyl group, amino group, epoxy group and thelike for improving adhesiveness and compatibility with epoxy resin. Thatthe resin is solid at room temperature is essential for controllingfluidity and providing desired film forming properties. This resin alsoaffords flexibility to the adhesive to improve thermal impact resistanceof the connected parts.

Examples of this type of resin are solid epoxy resin having a molecularweight of 800 or more, phenoxy resin, polyvinyl acetal, polyamide,polyester, polyurethane, ethylene-vinyl acetate copolymer, acrylicesters, acrylonitrile-butadiene rubber, styrene-butadiene rubber,styrene-isoprene rubber, styrene-ethylene-butylene copolymer and thelike which have been modified with a functional group such as mentionedabove.

(c) Micro-capsule type curing agent

The micro-capsule type or encapsulated curing agent used in the presentinvention comprises the core particles of a curing agent which aresubstantially coated or encapsulated with a film of a polymeric materialsuch as polyurethane, polystyrene, gelatin, polyisocyanate, etc., or aninorganic material such as calcium silicate or a thin film of a metalsuch as nickel, copper or the like.

The particle size is 10 μm or less, preferably 5 μm or less. The smallerthe average particle size, the more desirable for effecting a uniformcuring reaction.

As the curing agent forming the core, there can be used various types ofknown materials having reactivity with liquid epoxy resin or thefunctional group of solid resin or showing the action of a curing agent.

For example, as the curing agent having reactivity with epoxy resin,there can be used, for instance, aliphatic amine type, aromatic aminetype, carboxylic anhydride type, thiol type, alcohol type, phenol type,isocyanate type, tertiary amine type, boron complex type, inorganic acidtype, hydrazide type and imidazole type curing agents as well as themodified version thereof. Among them, tertiary amine type, boron complexsalt type, hydrazide type and imidazole type are preferred as thesetypes of curing agent allow quick curing and can minimize the necessityof giving considerations to the matters relating to chemical equivalencesince these curing agents are ionic polymerization type and actcatalytically. These curing agents can be used either singly or incombination.

The curing reaction is preferably completed when the connection isperfected, but it suffices if the reaction proceeds till a state isreached where the deformation of the pressure-deformable electrodes iskept between the circuits, and after-curing may be conducted in thisstate.

Regarding the type of encapsulated curing agent used in the presentinvention, the heat-activated type, namely the type which is ruptured inthe coating film under a certain temperature, is preferred to thepressure-activated type because use of the former type of curing agentallows obtainment of a more uniform reaction system to improvereliability of fine connections. The heat activation temperature of thecuring agent used in the present invention is preferably in the range of40° to 250° C. When the heat activation temperature is below 40° C., theadhesive film must be stored in a cold state because otherwise theretends to occur activation of the curing agent during storage. When theheat activation temperature is above 250° C., thermal damage may begiven to the parts or elements around the connected portion since a hightemperature is required in the connecting operation. For these reasons,the preferred range of heat activation temperature of the curing agentused in this invention is 70° to 200° C., more preferably 100° to 180°C.

The "heat activation temperature" referred to in this inventionrepresents the temperature at which the volume of heat generated becomesthe greatest when the adhesive composition is heated from normaltemperature to higher temperatures at a rate of 10° C./min by using adifferential scanning calorimeter (DSC).

As the micro-capsule type curing agent such as described above, thereare available and favorably usable the ones comprising particles of animidazole derivative having their surfaces inactivated with anisocyanate compound and the ones comprising particles of an aminecompound whose surfaces have been inactivated by reacting with an epoxyresin.

As for the amount ratios of said materials used for preparing anadhesive film according to the present invention, a liquid epoxy resin(a) is used in a ratio of 20 to 80% by weight, a solid resin having afunctional group (b) is used in a ratio of 80 to 20% by weight, and amicro-capsule type curing agent (c) is used in a ratio of 1 to 50 partsby weight based on the adhesive composition.

When the amount ratio of the liquid epoxy resin is less than 20% byweight and that of the solid resin is more than 80% by weight, nosatisfactory fluidity is obtained in the connecting operation and alsothe density of crosslinkage of the adhesive decreases, resulting inunsatisfactory heat resistance of the product.

The adhesive may contain where necessary an additive or additives suchas tackifier, filler, ultraviolet absorber, dispersant, anti-agingagent, polymerization inhibitor, coupling agent, etc.

In case the additive contained in the adhesive is a solid material andinsoluble and/or infusible in the adhesive composition, care should beexercised so that the adhesive won't adhere to the connected part ofelectrode to become an insulating spacer in the circuit connectingoperation.

Among the additives mentioned above, coupling agent is especiallyrecommended to use as it is effective for strengthening the adhesiveinterface of circuits, etc., to improve moisture resistance. (As thecoupling agent, known organic metal compounds such as chromium, silane,titanium, aluminum and zirconium compounds can be used.) Morespecifically, as examples of silane coupling agents which are mostcommonly used among said coupling agents, there can be citedvinyl-triethoxysilane, vinyltris(β-methoxyethoxy)silane,γ-methacryloxypropyltrimethoxysilane,γ-glycidoxy-propyltrimethoxysilane,β-(3,4-epoxycyclohexyl)ethyl-trimethoxysilane,N-γ(aminoethyl)-β-aminopropylmethyl-dimethoxy-silane,γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyl-trimethoxysilane,γ-mercapto-propyltrimethoxysilane, and γ-chloro-propyltrimethoxysilane.Among these coupling agents, those having an amino or epoxy group arepreferred from the viewpoint of improvement of adhesiveness to thecircuits.

The present invention has enabled electrical connection with highreliability by a simple process merely comprising application of heatand pressure by using an insulating adhesive layer with no need ofapplying an adhesive to a plurality of electrodes disposed at highdensity, owing to the specific features of the present invention thatthe projecting electrodes are deformable in the circuit connectingoperation and that a specific adhesive is applied in the form of a film.

According to the present invention, since the adhesive contains a liquidcomponent, it can be readily reduced in viscosity by heating in theconnecting operation, and when pressure is applied in this state, theadhesive is eliminated from between the electrodes and the correspondingcircuits to establish an electrical connection therebetween. Further,since the projecting electrodes are deformable under pressure,sufficient contact between electrode and circuit can be obtained, and itbecomes possible to conduct a live test in this state. Moreover, as theadhesive used in this invention contains encapsulated particles of aquick-curing type heat-reactive curing agent, the adhesive compositionis cured under pressure to provide a solid connection.

The curing agent used in the present invention is of a micro-capsuletype as described above, so that both requirements for good keepingquality and quick curing performance are satisfied to markedly improvethe workability. Also, because of small particle size which is less than10 μm, uniform curing at fine connections is made possible.

Thus, owing to said features of the present invention--that theprojecting electrodes are deformable under pressure and that the curingagent is heat-reactive, it is possible to simultaneously performelectrical connection and bonding of a great many electrodes andcircuits by a simple operation of heating under pressure.

Since the adhesive used in this invention is heat-curing type, thesubstrate may not necessarily be a light-pervious type; various othertypes of substrate can be used as well.

The solid resin in the adhesive serves for improving adhesiveness andcontrolling film forming properties or fluidity and also acts as aflexibilizer.

Also, since the adhesive is applied in the form of a film, no coatingstep is required and hence workability is bettered. Further, because ofuniform film thickness and a low volatile content, connection ofcircuits with high reliability becomes possible.

It is to be further noted that the adhesive film contains noelectroconductive particles and is composed of insulating substancesalone, so that this adhesive film involves no possibility of causingshort-circuiting between adjacent circuits by electroconductiveparticles and can well adapt itself to high-resolution circuits.

The superfluous adhesive after completion of connection is forced out ofthe electrode section, builds up at the periphery of IC chip and iscured, so that it serves as a sealant for the connected portion. Thisunnecessitates the sealing step and enhances connection reliability.

Since the silane coupling agents are low in molecular weight and mostlyliquid at normal temperature, the silane coupling agent in the adhesiveis capable of easy flowing at the electrode contact area and promotescontact between the circuits to reduce contact resistance in the circuitconnecting operation. After curing of the adhesive, said coupling agentacts as an electrode/adhesive interface reinforcing agent to contributeto the improvement of connection reliability.

The present invention will be further described below with reference tothe examples thereof, in which "%" and "parts" are by weight.

EXAMPLES 1-8

(1) Preparation of adhesive film

The materials shown in Table 1 were mixed so that the involatile contentof the mixtures exclusive of micro-capsule type curing agent will havethe weight ratios shown in Table 2. Then each mixture was heated andmelted at about 180° C.

Viscosity of each mixture at 180° C. was below 10 P. Each mixture wasadded gradually with toluene under cooling to obtain a 50 wt % adhesivesolution. To this solution were added a specified amount (shown in Table2) of micro-capsule type curing agent and 1 part by weight of anadditive A-186 to prepare an adhesive solution.

The micro-capsule type curing agent shown in Table 1 is a commerciallyavailable masterbatch prepared by using an imidazole type curing agentas core material, coating the particle surfaces thereof with apolyurethane material to a thickness of several hundred Å to formmicro-capsules of curing agent having an average particle size of 4 μm,and dispersing them in a bisphenol type liquid epoxy resin in a weightratio of 1:2. 1.5 Mg of this masterbatch was weighed out, and the peaktemperature (activation temperature) in DSC (Du Pont 1090) which wasreached when heating said masterbatch at a rate of 10° C./min from 30°C. was shown in Table 1.

In the present invention, it is assumed that the amount of liquid epoxyin said masterbatch curing agent is discounted in the content of liquidepoxy in the film composition.

                                      TABLE 1                                     __________________________________________________________________________    Trade      Brevity                                                            name       code                                                                              Maker     Substance                                            __________________________________________________________________________    Liquid                                                                             Qautlex                                                                             1010                                                                              Dow Chemical Co.,                                                                       Bisphenol type (high purity; hydrolytic              epoxy                                                                              1010      Ltd.      chlorine: less than 100 ppm)                         resin                                                                              Qautlex                                                                             2010                                                                              Dow Chemical Co.,                                                                       Phenol novolak type (high purity;                         2010      Ltd.      hydrolytic chlorine: less than 100 ppm)              Solid                                                                              Phenoxy                                                                             PKHH                                                                              UCC       Phenoxy resin, Mw = about 10,000                     resin                                                                              PKHH                (representative functional group (rfg):                                       hydroxyl group)                                           Epikote                                                                             1009                                                                              Yuka Shell Epoxy                                                                        Bisphenol type epoxy resin, Mw = about                    1009      Co., Ltd. 3,709 (rfg: epoxy group)                                  Butyral                                                                             3000                                                                              Denki Kagaku Kogyo                                                                      Acetal resin (rfg: hydroxyl gorup)                        3000K     K.K.                                                                Tuftec M-                                                                           1913                                                                              Asahi Chemical                                                                          Carboxy-modified styrene-ethylene-butylene                1913      Industry Co., Ltd.                                                                      block copolymer (rfg: carboxyl group)                     Bylon 300                                                                           300 Toyobo Co., Ltd.                                                                        Polyester resin (rfg: hydroxyl group)                Micro-                                                                             Novacure                                                                            3721                                                                              Asahi Chemical                                                                          Imidazole type (activation temp.: 105°                                 C.).                                                 capsule                                                                            HX-3721 HP                                                                              Industry Co., Ltd.                                                                      Dispersant epoxy is a high-purity product.           type Novacure                                                                            3741                                                                              Asahi Cehmical                                                                          Imidazole type (activation temp.: 145°                                 C.)                                                  curing                                                                             HX-3741   Industry Co., Ltd.                                             agent                                                                         Additive                                                                           A-186 186 Nippon Unicar Co.,                                                                      β-(3,4-Epoxycyclohexyl)ethyltrimethoxy-                        Ltd.      silane                                               __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    Adhesive film composition (nonvolatile content                                                                 Properties                                   in weight ratio)                         Gela-                                Liquid                     Micro-    Vola-                                                                             tion                                                                              Hydrolytic                       epoxy                      capsule type                                                                        Thick-                                                                            tile                                                                              time                                                                              chlorine ion                     resin      Properties      curing agent                                                                        ness                                                                              content                                                                           Sec. at                                                                           concentration                    No.  1010                                                                             2010                                                                             PKHH                                                                              1009                                                                             3000                                                                             1913                                                                             300                                                                              3721                                                                             3741                                                                             (μm)                                                                           (%) 180° C.                                                                    ppm                              __________________________________________________________________________    Example                                                                            20    80              20    25  0.012                                                                             10  3.3                              Example                                                                            65    35              20    25  0.008                                                                             5   0.3                              2                                                                             Example                                                                            65    35                 20 25  0.012                                                                             18  2.5                              3                                                                             Example 50 50                 20 25  0.010                                                                             15  2.8                              4                                                                             Example 50     50             20 25  0.014                                                                             8   2.1                              5                                                                             Example 50        50          20 25  0.012                                                                             9   3.5                              6                                                                             Example 50           50       20 25  0.051                                                                             11  3.0                              7                                                                             Example 50              50    20 25  0.10                                                                              12  4.8                              8                                                                             __________________________________________________________________________

Each of the prepared adhesive solutions was coated on a separator (a 100μm thick Teflon film) to a predetermined thickness by a bar coater anddried at 80° C. for 20 minutes to obtain an adhesive film.

To examine the property deterioration during storage, the obtainedadhesive films were subjected to a preservation test after a 24-hourheat treatment at 50° C. (corresponding to about one-month heattreatment at 25° C.), but each of the films was in a usable state andshowed good keeping quality.

The properties of the above adhesive films are shown in Table 2.

The values of "thickness" shown in the table are the ones measured byusing a micrometer having a precision of 1 μm. The "volatile content"denotes the rate of change of weight after treatment when a 10 mm squaresample film was subjected to a thermal decomposition treatment orchromatography under the conditions of 100° C. and 3 minutes. "Gelationtime" was measured by a 180° C. platen method according to JIS K-7071."Hydrolytic chlorine ion concentration" was determined by subjecting a100 mm square sample to one-hour heating and curing in a 150° C.thermostat, then peeling off the separator, treating theseparator-removed sample in 100 ml of pure water at 100° C. for 10hours, and analyzing the extract by an ion chromatograph (Dionex 2010i).

(2) Connection

There were prepared the wiring boards each of which had formed on aglass plate the chrome circuits having connecting terminals incorrespondence to the bump disposal on a semiconductor chip (5 mmsquare, 0.5 mm high, having 50 μm square and 20 μm high solder bumpshaving their surfaces gold plated to a build-up of 0.2 μm at 200positions along the periphery of the main face).

Said adhesive films were positioned between the bump surfaces ofsemiconductor chip and the corresponding circuit surfaces of wiringboard. The adhesive films of Examples 2 to 8 were capable of easyprovisional adhesion to the semi-conductor surface as these films hadtackiness at room temperature. In the case of the film of Example 1, asit had no tackiness at room temperature, provisional adhesion was madeby heating the glass circuits to about 70° C.

Separator was peeled off after said provisional adhesion, andpositioning of glass circuits and bumps was conducted from the glasscircuit side under a microscope. Then the assembly was subjected to180°C./30 kgf/cm² heating and pressing for 30 seconds.

In the above process of connection, there was observed efflux of theadhesive to the periphery of the chip in the early phase of the process,while in the later stage of the process there was noted progress ofbodying-up by gelation (5-18 seconds at 180° C.) of the adhesive withactivation of the micro-capsule type curing agent.

(3) Evaluation

Electric conduction check-up tests of the connected products showed goodconnection in each product. Also, the product obtained in each of theabove Examples maintained good connection even after 100 hours ofpressure cracker test at 120° C.

Scanning electron microscopic observation of the cross-sections of theconnected portions showed that contact between projecting electrodes andcircuits has been made in a satisfactory way. It could be also confirmedthat all of the projecting electrodes were equally flattened andcontacted with the corresponding circuits, with the long-legged ones ofthe projecting electrodes being given a greater degree of deformation sothat they would become flush with other electrodes.

The main constituent of projecting electrode, or bump, is a soldercomposed of Sn and Pb in a ratio of 60 to 40, and the melting pointthereof measured by DSC was 190° C. which is close to the temperature(180° C.) applied at the time of circuit connection. Because of thisfact and thin build-up of gold plating, it is considered thatdeformation was evoked by pressure applied in the circuit connectingoperation.

The periphery of the chip was covered with the effused adhesive. Itseems that the adhesive served as a moisture protector as it containedno electroconductive particles, and the adhesive film showed asufficient moisture resistance to stand PCT without any particularsealing treatment.

The connected chips were free of dents or cracks and had goodconnection. This is considered due to the fact that the adhesivecontained no hard substance such as electroconductive particles.

EXAMPLE 9

The adhesive film obtained in Example 8 was stuck, by making use of itstackiness and by using a rubber roller, to the pressure-deformableelectrodeformed surface of a 76 mm in diameter wafer to be made intosemiconductor chips used in Examples 1-8. This adhesive-applied waferwas secured to a fixed plate of a dicing device by vacuum suction andcut along with the adhesive layer by a dicing saw at a speed of 3,000r.p.m. to form 5 mm square chips. In this operation, the dicing sawwhich has run through the adhesive layer reached a part of theseparator, but since curing of the adhesive film has scarcely advanced,the wafer and adhesive were securely held together with a sufficientadhesive force. The large thickness (100 μm) of the separator alsoconducted to the prevention of scattering of chips.

Separator was removed from the adhesive-applied chips obtained in themanner described above, and the latter were subjected to the sameconnecting operation and evaluation as conducted in Examples 1-8. Goodelectrical and mechanical connections could be obtained in this Example,too.

EXAMPLE 10

(1) Preparation of adhesive

Epikote 1004 (bisphenol type epoxy resin, Mw=about 1,600, mfd. by YukaShell Epoxy Co., Ltd.), Nipol 1072 (carboxy-modified nitrile rubber,mfd. by Nippon Geon Co., Ltd.) and Novacure 3742 HP (a masterbatch typecuring agent prepared by coating the core particles of an imidazole typecuring agent with a polyurethane type material to form "micro-capsules"of curing agent having an average diameter of 2 μm, and dispersing themin a highly purified liquid bisphenol type epoxy in a weight ratio of1:2; activation temp.: 125° C., mfd. by Asahi Chemical Industry Co.,Ltd.) were blended in a ratio (by solid content) of 40:20:40, and themixture was further added with 0.5 part of A-187(γ-glycidoxypropyltrimethoxysilane, mfd. by Nippon Unicar Co., Ltd.) and0.1 part of A-1100 (γ-aminopropyltriethoxysilane, mfd. by Nippon UnicarCo., Ltd.) to prepare a 30% toluene solution.

This solution was coated on a separator by a roll coater in the same wayas in Examples 1-8 and dried at 90° C. for 10 minutes to obtain a 20 μmthick adhesive film. The property evaluation of this film conducted inthe same way as in Examples 1-8 gave the following results: volatilecontent=0.013%; gelation time=13 seconds; hydrolytic chlorine ionconcentration after curing=2.9 ppm.

(2) Connection

A substrate circuit assembly was prepared by forming on a glasssubstrate the ITO/Cr circuits with connecting terminals incorrespondence to the bump disposal on each semi-conductor chip (5 mmsquare and 0.5 mm high, having 100 gold bumps (100 μm square and 15 μmhigh) along the periphery of the main face).

Said adhesive film was bonded on the substrate circuit assembly and,after separating the polypropylene film, positioning of the bumps ofsaid semiconductor chips and the corresponding terminals on thesubstrate was made from the substrate circuit (glass substrate) sideunder a microscope, placing 10 semiconductor chips on one glasssubstrate. In this state, heating (80° C.) and pressing (20 kgf/cm²)were conducted, and an electrical conduction test was made with amultimeter by passing an electric current of 10 μA through the substratecircuits by using a measuring probe.

(3) Regeneration

In said electrical conduction test, abnormality was detected in one ofthe ten semiconductor chips. So, after removing pressure, the defectivepart was debonded and replaced with a new chip and the same live test asdescribed above was conducted. In this case, no abnormality was found.Debonding of the abnormal part was very easy since the adhesive was in ahalf-cured film-like state, and the debonded area was clean.

(4) As no abnormality was detected in the live test under pressure, theunderside of the pressing plate was heated at 190° C. (at highest) for10 seconds by an infrared irradiator. This infrared irradiator isdesigned to condense light from heat source (xenon lamp) through a lensand the light can be led close to the connected portion by optical fiberin a state almost free of loss, so that it is possible to raise or lowertemperature in a short time.

In this Example, live test was possible as the adhesive kept at atemperature below the activation temperature of curing agent in theadhesive was pressed in a half-cured state.

Also, owing to use of an infrared irradiation and condensation system ascuring means at the time of connection, it was possible to raisetemperature in a short time and complete the adhesive curing reactionwhile maintaining the pressed state at the time of live test.

According to the present example, since the live test can be conductedby keeping the adhesive in a half-cured state, regeneration of faultyparts can be effected very easily and it becomes possible to save energyin the process and to reduce the production cost.

As described above, the present invention, which is featured bydeformability of projecting electrodes and use of a specific adhesivefilm, enables connection of high-density circuits with high reliability.

What is claimed is:
 1. A process for electrically connecting circuits byinterposing an insulating adhesive between opposing circuits to beconnected, at least one of said circuits formed on an insulating layerhaving a plurality of electrodes projecting from a main face, saidprojecting electrodes being provided three or more on the average at theperiphery or on the entirety of the main face, said projectingelectrodes having fine unevenness at a convex end, and said projectingelectrodes being deformable under pressure in the circuit connectingoperation, and said adhesive comprising as essential components a highlypure liquid epoxy resin reduced in concentration of impurity ions orhydrolytic chlorine ions to a level below 300 ppm for each impurity, asolid resin having a functional group, and a micro-capsule type curingagent having a heat activation temperature of 70° to 200° C., and saidadhesive being in the form of a film having a thickness of 50 μm or lessand a volatile content of 0.5% or less, wherein the adhesive is removedfrom contact areas of the projecting electrodes and opposing circuitsdue to lowering in viscosity of the adhesive and is substantially curedafter the projecting electrodes have been contacted with the opposingcircuits by applying heat and pressure at the time of connection withheating at 70° to 200° C. for 60 seconds or less per one electrode undera pressure of 1 kgf/cm² or less per one electrode.
 2. A processaccording to claim 1, wherein a live test is conducted while applyingpressure to the semiconductor chips and substrate circuits and keepingthe adhesive in a half-cured state, and then the adhesive is cured underheating and pressure.
 3. A process according to claim 1, wherein thecuring agent is an imidazole derivative.
 4. A process according to claim1, wherein the solid resin is a solid epoxy resin, a polyvinyl acetal, apolyamide, a polyester, a polyurethane, an ethylene-vinyl acetatecopolymer, an acrylic ester resin, an acrylonitrile-butadiene rubber, astyrene-butadiene rubber, a styrene-isoprene rubber, or astyrene-ethylene-butylene copolymer.
 5. A process according to claim 1,wherein the adhesive further comprising an organic metal compound as acoupling agent.
 6. A process according to claim 1, wherein the curingagent is an aliphatic amine, an aromatic amine, a carboxylic anhydride,a thiol, an alcohol, a phenol, an isocyanate, a tertiary amine, a boroncomplex, an inorganic acid, a hydrazide, an imidazole or a mixturethereof.
 7. A process for electrically connecting circuits byinterposing an insulating adhesive between opposing circuits to beconnected, at least one of said circuits formed on an insulating layerhaving a plurality of electrodes projecting from a main face, saidprojecting electrodes being deformable under pressure in the circuitconnecting operation, and said adhesive comprising (a) a highly pureliquid epoxy resin, (b) a solid resin having a functional group, and (c)a micro-capsulated or encapsulated curing agent for the epoxy resin witha heat activation temperature of said adhesive 70° to 200° C., and saidadhesive being in the form of a film having a thickness of 50 μm or lessand a volatile content of 0.5% or less, wherein the adhesive is removedfrom contact areas of the projecting electrodes and opposing circuitsdue to lowering in viscosity of the adhesive and then adhesive issubstantially cured after the projecting electrodes have been contactedwith the opposing circuits by applying heat and pressure at the time ofconnection with heating at 70° to 200° C. for 60 seconds or less under apressure of 1 kgf/cm² or less per one electrode.
 8. A process accordingto claim 7, wherein the curing agent is an aliphatic amine, an aromaticamine, a carboxylic anhydride, a thiol, an alcohol, a phenol, anisocyanate, a tertiary amine, a boron complex, an inorganic acid, ahydrazide, an imidazole or a mixture thereof.
 9. A process according toclaim 7, wherein the adhesive further comprises an organic metalcompound as a coupling agent.